ABSTRACT

It is well known that the replacement of round tubes to oval tubes in a fin-and-tube heat exchanger reduces the air-side pressure drop as well as the low-performance region behind the tube, which improves the thermal performance of the heat exchanger. However, experimental evidences are lacking, especially for generic heat exchangers. In this study, generic heat exchangers having oval tubes were tested, which included two different oval tube dimension and two different tube pitches. Round tube samples were also tested for a comparison purpose. The effect of fin pitch on j factor was negligible, whereas f factor increased as the fin pitch increased. Furthermore, both the j and f factor decreased as the number of tube row increased. A thermal performance comparison based on the ratio of thermal conductance per unit volume (${\eta }_o{h}_o{A}_o/V_o$) to pressure drop per unit length ($\mathrm{\Delta }P/L$) revealed that the oval tube samples yielded a higher performance than the round tube samples, except at a small number of tube row. Furthermore, the best performance was obtained from the oval tube samples having a smaller diameter tube. On the other hand, relatively poor performance was obtained from the oval tube samples having a larger diameter tube, probably due to the large pressure drops. The j and f correlations were developed based on the data.

摘要

众所周知，在翅片管式换热器中，将圆管换成椭圆管可以减少空气侧压降以及管后的低性能区域，从而提高换热器的热性能。 . 然而，缺乏实验证据，特别是对于通用热交换器。在这项研究中，测试了具有椭圆管的通用热交换器，其中包括两种不同的椭圆管尺寸和两种不同的管间距。为了比较的目的，还测试了圆管样品。翅片节距对j因子的影响可以忽略不计，而f因子随着翅片节距的增加而增加。此外，j和f系数随着管排数的增加而减小。基于单位体积热导率的热性能比较 (${\eta }_{○}{H}_{○}{\mathrm{一种}}_{○}/{五}_{○}$) 到每单位长度的压降 ($\mathrm{\Delta }磷/\mathrm{大号}$) 显示椭圆管样品比圆管样品产生更高的性能，除了管排数量较少。此外，从具有较小直径管的椭圆管样品中获得了最佳性能。另一方面，从具有较大直径管的椭圆管样品获得相对较差的性能，这可能是由于大的压降。j和f相关性是基于数据开发的。